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adventures into the land of the command line

network troubleshooting tools

checking the localhost’s network interface information

$ ifconfig -a

ping an ip address or a domain name for a response. ping sends ICMP echo request packets to a destination

$ ping ipaddress/domainname

Netcat is a simple Unix utility which reads and writes data across network connections, using TCP or UDP protocol. to create a TCP connection to the given port on the given target host

$ nc -v -w 1 ipaddress port

-v = verbose
-w = timeout, will silently close connection if timeout is greater than 1 second

test connectivity to an ip address and port

$ telnet ipaddress port

provide information about the path a packet takes. traceroute sends packets to a destination, asking each Internet router along the way to reply when it passes on the packet. This will show you the path packets take when you send them between your location and a destination

$ traceroute ipaddress/domainname

look up the IP addresses associated with a domain name

$ nslookup domainname

displays incoming and outgoing network connections on your computer, which programs are making which connections, how much data is being transmitted, and other information

$ netstat -a

capture, sniff and inspect network packets

solaris:

$ snoop -d eth0 -o /tmp/somefile.cap

-d = device, choose a network interface
-o = output to a file

rhel:

$ tcpdump -s0 -A -i any port 80 | tee /tmp/output

-s = snarf or snaplength, truncates the length of each line to number of bytes. (chars). 0 = required length of whole packet, do the whole lot.
-A = Print each packet (minus its link level header) in ASCII.  Handy for capturing web pages.
-i = choose a network interface, any is all of them
port = filter by things coming on a specific port